There is probably no phrase associated with the jhānas that has resulted in more confusion than "Vipassanā Jhānas." The phrase is usually used in contrast to "Samatha Jhānas" which refers to the jhānas as described either in the Suttas or in the Visuddhimagga. I have heard the Vipassanā Jhānas defined at one time or another as each of the following:

1. you're doing vipassanā practice and some of the jhāna factors occur, but you are not concentrated enough to call the experience a "Samatha Jhāna,"

3. you're doing vipassanā practice and use that to generate access concentration and enter the Samatha Jhānas,

4. you're practicing one of the Samatha Jhānas and gain some insight while in that jhāna, therefore that jhāna has become a Vipassanā Jhāna,

5. the Vipassanā Jhānas are four of the sixteen Insight Knowledges (Vipassanā Ñāṇas) in the progress of insight.1

But none of these definitions ever made any sense to me! For #1, why call it a jhāna at all if you only have factors happening without enough concentration to call it a jhāna? For #2 and #3, why make a distinction based on access method if the jhānic experience is the same as a so-called "Samatha Jhāna?" For #4, why change the name of an experience based on something that occurred during that experience but that did not change that experience? For #5, which four knowledges, and why only four, and why those four?

It turns out that definition #5 is the official definition  but the questions above still apply. There definitely seems to be a consensus that the 4th Vipassanā Jhāna is the "Knowledge of Equanimity about Formations" since both this knowledge and the "4th Samatha Jhāna" have equanimity as their most obvious characteristic. But what are the first three Vipassanā Jhānas referring to? None of the knowledges seem to involve pīti or sukha in any way whatsoever. In fact the Knowledges of Terror, Danger, Disenchantment and Desire for Deliverance are quite the opposite of anything associated with sukha! What's going on here? Furthermore the jhānas  the so called Samatha Jhānas  do occur in the Seven Stages of Purification in the second stage, while the Insight Knowledges occur in the third through seventh stages. And why use the word "jhāna?" The literal meaning of jhāna is "meditation" and the knowledges are neither ways to meditate nor are they concentration states, they are knowledges.

Finally after many years of hearing about the Vipassanā Jhānas, reading about the Vipassanā Jhānas, listening to dhamma talks about the Vipassanā Jhānas, it occurred to me that most likely something like the following happened sometime in the long forgotten past:

An eminent monk got up before a group of junior monks and said "Tonight I will teach you about the Vipassanā Ñāṇas." And some little monklet heard "I will teach you about the Vipassanā Jhānas." That monklet learned about the Vipassanā Ñāṇas, but thought he was learning about the Vipassanā Jhānas. Eventually that monklet grew up to be an eminent monk and began teaching about the Vipassanā Ñāṇas using the phrase "Vipassanā Jhānas." And so today we have the ill-defined concept of Vipassanā Jhānas that haphazardly refers to 4 of the Vipassanā Ñāṇas.

Now remember, the above is totally conjecture on my part! The phrase "Vipassanā Jhānas" does appear in some of the later commentaries, but never have I found it to have a clear referent, nor have I found any reason to use the word "Jhāna" in association with the Ñāṇas, nor have I found it useful in any way. This overloading of the term "jhāna" seems to serve no purpose except to generate confusion. So when someone asks me "What are the Vipassanā Jhānas?" I have to answer "A mishearing of the phrase Vipassanā Ñāṇas."

Of course, there are others who do find the phrase "Vipassanā Jhānas" useful. If you don't find my explanation above satisfactory, you'll need to talk to people who do feel the phrase "Vipassanā Jhānas" does actually refer to something useful.